City won their final game of the league season 3-0 at home to Preston, with Lee Trundle scoring his first goal from open play since October.
The victory was only the Robins second in their last 11 games.
But despite such patchy form, Johnson says his team will be in good spirits ahead of their trip to Selhurst on Saturday.
"We know what to expect from any Neil Warnock side, and Palace are in very good form," he said. "But we are proud of finishing fourth in the Championship after 46 games and will go there next Saturday in confident mood."
Striker Lee Trundle agreed, saying: "Palace are probably the toughest side we could have met in the play-offs, but we will go there with confidence restored and looking to win the first leg."